The present invention relates to a magnetic recording medium adapted for use in magnetooptical memory, magnetic recording, display device or the like, and more particularly to an improvement in a magnetooptical recording medium allowing regeneration of recorded information by means of magnetooptical effect such as magnetic Kerr effect or Faraday effect.
For use as the recording layer of magnetooptical recording medium, there have conventionally proposed polycrystalline films such as MnBi or MnCuBi, amorphous films such as GdCo, GdFe, TbFe, DyFe, GdTbFe, TbDyFe, GdFeCo, TbFeCo or GdtbCo, and single crystal films such as GdIG.
Among these films, the aforementioned amorphous films are recently considered most preferable for use as the recording layer of magnetooptical recording medium, in consideration of the film forming property at the formation of a film of a large area at a nearly ambient temperature, the recording efficiency for recording signals with a small optothermal energy, and the readout efficiency for regenerating the recorded signal with a high S/N ratio. Particulary GdTbFe is most preferred as the recording layer of the magnetooptical recording medium because of a large Kerr rotation angle and a Curie point in the range of 150.degree. C.
However the amorphous magnetic materials employed in the magnetic recording medium, including GdTbFe, are generally associated with a drawback of poor anticorrosive resistance. Lack of reliable stability is the largest problem of these materials as they show deterioration in the magnetic properties when maintained in contact with air and water vapor and are eventually oxidized completely to transparent state.
In order to resolve the above-mentioned drawback it is necessary, in addition to the improvement in the magnetic material itself, to isolate the recording layer, consisting of such magnetic material, from air (particularly oxygen) and moisture which are the cause of said deterioration. Such isolation can be most conveniently achieved by covering the recording layer with a material of low permeation of air and moisture, and various materials have been proposed for use in such protective layer. Examples of such materials are oxides such as ZnO, MgO, Al.sub.2 O.sub.3, SiO (disclosed in the Japanese Patent Laid-open No. 110056/1984), SiO.sub.2, ZrO.sub.2, CeO.sub.2, In.sub.2 O.sub.3, SnO.sub.2, TiO.sub.2, LiNbO.sub.3 or LiTaO.sub.3, fluorides such as MgF.sub.2, CaF.sub.2 or CeF.sub.4, and nitrides such as Si.sub.3 N.sub.4 or ALN (disclosed in the Japanese Patent Laid-open No. 110052/1984). Also known is the use of a coating, obtained with an appropriate solvent, of an organic resin such as polypropylene, polyethylene, polyamide, polyacrylonitrile, vinylidene chloride, polycarbonate, ethylene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, vinylidene chloride-acrylonitrile copolymer etc., or of a plasma-polymerized film of fluorocarbon as disclosed in the Japanese Patent Laid-open No. 90246/1984.
Among these conventional protective films, inorganic ones consisting of oxides or fluorides are advantageous because of simple film formation by a dry process such as vacuum evaporation or sputtering, but are still deficient in the insulation of air and moisture, thus being unable to achieve satisfactory prevention of deterioration of the recording layer. On the other hand, the coating of organic resins not only requires a complex wet process involving the use of solvents, but also is associated with fluctuating properties of the obtained protective layer.
The plasma-polymerized film is ideal for the protective layer because it can be formed in a dry process and is little permeated by air and moisture. However, though such plasma-polymerized film can be satisfactorily formed under the recording layer as disclosed in said Japanese Patent Laid-open No. 90246/1984, formation of such film on the recording layer gives rise to a reaction between the monomer gas and the magnetic layer in the course of plasma polymerization process, often resulting in a deterioration of the magnetic properties.
The object of the present invention, therefore, is to provide a magnetic recording medium with a significantly improved anticorrosive resistance, without sacrificing the magnetic properties of the recording layer.
The above-mentioned object can be achieved according to the present invention by forming a plasma-polymerized film on a recording layer with an intermediate layer therebetween.